| dc.description.abstract | The biological pump is a critical process in the oceanic carbon cycle, transferring organic carbon from the atmosphere and surface waters into the deep ocean and seafloor sediments. Organic carbon stored in living biomass can be exported into deep sea areas via deadfalls, potentially getting stored for hundreds of years, but studies disagree on the amount of carbon they store, and their significance towards the total carbon flux in the ocean. In this study, organic carbon export of marine mammal deadfalls was calculated from existing data on abundance, biomass, residency, mortality rates, and organic carbon content. This study’s area is set in the Nordic Seas, a part of the Northeast Atlantic Ocean, and consists of three regions; ICE (Icelandic shelf, Denmark Strait, Iceland Sea), GN (Greenland Sea and Norwegian Sea), and BS (Barents Sea), that has been comprehensively studied for marine mammal abundance estimates. Previous carbon export studies on marine mammals have mainly focused on baleen whales, but the contribution of the more abundant, smaller marine mammals such as pinnipeds and cetaceans, as well as sperm whales, may also be relevant. The total annual organic carbon flux potential was estimated to be 2.68 × 10−5 Pg C yr−1 (95% CI 1.23−5.23 × 10−5 Pg C yr−1), which equals ~26 887 tonnes C yr−1 for all species across the three study regions. Fin whales (Balaenoptera physalus) were the largest single species contributor with ~8 653 tonnes C yr−1 (95% CI 5 234−12 072 tonnes C yr−1). Harp seals (Pagophilus groenlandicus) were the second largest with ~5 072 tonnes C yr−1 (95% CI 3 329, 6 815 tonnes C yr−1) and common minke whales (Balaenoptera acutorostrata) were the third with 3 613 tonnes C yr−1 (95% CI 2 252, 4 974 tonnes C yr−1). The largest organic carbon flux took place in the ICE region, with over half (51%) of the total contribution of organic carbon located within this region. Compared to organic carbon export by dissolved organic carbon (DOC) and particulate organic carbon (POC), the carbon flux potential derived from marine mammal deadfalls in this study are about 0.03−0.07% and 0.019−0.042% of these values, respectively. While regional storage potentials are low compared to other sources of organic carbon flux, local effects on organic carbon accumilation are massive, with an increase of ~2.14×1010 % per m2 compared to POC export. This study provides the first estimate of organic carbon export via marine mammal deadfalls in the Northeast Atlantic and is the first study to consider the wide range of marine mammals, from pinnipeds and small cetaceans to large whales, in a deadfall carbon export calculation. The study shows the importance of understanding the role of marine mammals in the oceanic carbon cycle, and to quantify the carbon export contribution from different components of the ecosystem in today’s climate crisis. | |
